This proposal represents the doctoral work of Elizabeth Corder, MPH. Dr. Harry Guess is Ms. Corder's dissertation advisor and will serve as the principal investigator. Drs. Barbara Hulka, Gary Friedman, Stephen Sidney, Norman Orentreich, Joseph Vogelman, Marc Drezner, and Robin Vollmer are coinvestigators. The proposed nested case-control study evaluates the relationship of prediagnostic serum concentrations of 25-hydroxyvitamin D (25-D) and 1,25- dihydroxyvitamin D (1,25-D) with the incidence of prostate cancer in a defined population controlling for age, race, clinic location, and the seasonal variation in 25-D. Prior to December 31, 1987, there were 782 incident cases of prostate cancer among Kaiser Permanente Health Plan members who underwent routine multiphasic examination in Oakland or San Francisco between 1964 and 1971. From randomly selected and verified by pathologic review. Each case will be race and age matched to a single control examined at the same location within two weeks of the case. Concentrations of 25-D and 1,25-D in serum specimens obtained at the examination constitute exposure. Analysis will address the following questions: Do concentrations of 25-D and 1,25-D differ between cases and controls? To what extent can the higher incidence rates among blacks and older men be attributed to differences in vitamin D concentrations compared to whites and younger men, respectively? Do cases with higher baseline levels have less anaplastic tumors at diagnosis? If so, is this reflected in improved survival? These questions are of both theoretical and clinical importance in that they should provide insight into the etiology of prostate cancer as well as generate hypotheses concerning its prevention and treatment.